Channels and keys of animated bones do not appear on Graph Editor
Problem answered here:
Graph Editor does not show any keyframes

Apparently the button "show_hidden" on the view controls at the botton on Graph Editor must be set to true to allow the visualization of keys from objects or bones that are "hidden". To the right is the button "show_only_errors" to show only keys with errors or a red bar under (usually unupdated or related to a deleted object/bone/shape key) and to the left is the button "show_only_selected" for showing only keys from objects you selected, which if set to "false" makes all keys from any object and bone appear.


*Examples made from Blender 2.79b. The buttons do the same thing and are on the same place on the newest Blender's version to date

I cannot explain the status of "hidden" yet. It doesn't seem to have anything to do with "hidden from view", it is another type of "hidden"